Spatially resolving the hot CO around the young Be star 51 Ophiuchi

TL;DR

This study spatially resolves the hot CO emission region around the young Be star 51 Ophiuchi, revealing it originates in a compact, dust-free gaseous disk closer to the star than the dust sublimation radius.

Contribution

First spatially resolved the CO bandhead emission region around 51 Ophiuchi using interferometry, confirming its origin in a hot gaseous disk inside the dust sublimation radius.

Findings

CO emission region is at ~0.15 AU from the star

Continuum emission region is at ~0.25 AU, further out

Hot gas inside dust sublimation radius contributes to near-infrared emission

Abstract

51 Oph is one of the few young Be stars displaying a strong CO overtone emission at 2.3 microns in addition to the near infrared excess commonly observed in this type of stars. In this paper we first aim to locate the CO bandheads emitting region. Then, we compare its position with respect to the region emitting the near infrared continuum. We have observed 51 Oph with AMBER in low spectral resolution (R=35), and in medium spectral resolution (R=1500) centered on the CO bandheads. The medium resolution AMBER observations clearly resolve the CO bandheads. Both the CO bandheads and continuum emissions are spatially resolved by the interferometer. Using simple analytical ring models to interpret the measured visibilities, we find that the CO bandheads emission region is compact, located at $0.15_{-0.04}^{0.07}$AU from the star, and that the adjacent continuum is coming from a region further away $0.25_{-0.03}^{0.06}$AU. These results confirm the commonly invoked scenario in which the CO bandheads originate in a dust free hot gaseous disk. Furthermore, the continuum emitting region is closer to the star than the dust sublimation radius (by at least a factor two) and we suggest that hot gas inside the dust sublimation radius significantly contributes to the observed 2 $\mu$m continuum emission.